Partial molar volumes of ionic and nonionic organic solutes in water: A simple additivity scheme based on the intrinsic volume approach

Partial molar volumes at infinite dilution, V degrees, in water at 25 degrees C for organic electrolytes and nonelectrolytes are described through a simple additivity scheme based on the intrinsic volume approach. The contributions to V degrees of hydrocarbon groups were determined from the "experimental" CH2 increment assuming that all hydrocarbon portions have the same packing efficiency in aqueous solution. Twenty-two charged and 51 uncharged groups, are assigned a V degrees contribution and the partial molar volumes of nearly 400 monofunctional organic solutes are reproduced with a root mean square deviation of 0.9 cm(3)-mol(-1). The different volumetric behavior of linear, branched, and cyclic molecules is discussed. A comparison is made of uncharged (hydrocarbon and polar) with charged groups, as well as of groups with small molecules and ions. A relative estimate is given of the volume effects (cavity formation, hydrophobic hydration, solvent shrinkage, H bonding, and electrostriction) involved in the interaction of hydrophobic and hydrophilic groups with water. Deviations from additivity for mono- and polyfunctional solutes, including polyelectrolytes, are analyzed in terms of(I) extension of the hydration cosphere of different polar centers; (2) intramolecular interactions and their dependence on nature, number, and mutual distance of interacting groups. The van der Waals volume V-W is extensively used as molecular descriptor. Estimates of V-W for both charged and uncharged groups are presented.